1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least an inductive magnetic transducer and to a fabrication method for such a thin-film magnetic head, and further, to a head gimbal assembly and hard disk device which contain a thin-film magnetic head.
2. Description of the Related Art
Dramatic advances have been continuing in the areal density of hard disk devices, and recent years, the areal densities in the range of 100 gigabits per square inch have been realized. As a thin-film magnetic head, a composite thin-film magnetic head is widely used which has both a reproducing head having a magnetoresistance (MR) element for reproducing and a recording head having an inductive magnetic transducer for writing. For the improvements in areal density of such a composite thin-film magnetic head, improvements in performance both for reproducing and recording are necessary. An anisotropic magnetoresistance (AMR) elements which employ anisotropic magnetoresistance has been shifted to giant magnetoresistance (GMR) elements which employ giant magnetoresistance as a means of improving the reproducing capabilities.
Recording to a medium is realized by sending a current which changes in accordance with the content to be recorded to a coil, then magnetizing the medium by the magnetic field leaked from magnetic poles which are magnetized based on the principle of electromagnetic induction. In order to realize this principle, the recording head is provided with: two opposing magnetic pole tips which confront each other at an air bearing surface of the head, a lower magnetic layer and an upper magnetic layer which respectively include each of these tips, a recording gap layer which is provided between the magnetic pole tip of the lower magnetic layer and the magnetic pole tip of the upper magnetic layer, and a thin-film coil insulated from the lower magnetic layer and the upper magnetic layer. Increasing the areal density further requires miniaturization especially of the lower magnetic layer, the upper magnetic layer, and the recording gap layer.
One major problem which accompanies miniaturization of a magnetic head of this construction is the variations in fabrication accuracy. A thin-film magnetic head is fabricated through the use of semiconductor fabrication technology in which one wafer is used to simultaneously fabricate a plurality of thin-film magnetic heads. Suppressing the variation in the magnetic pole width of a plurality of thin-film magnetic heads which are fabricated from one wafer becomes difficult when the effective recording track width is reduced to 0.3 μm or less.
Technology for fabricating a thin-film magnetic head having a small magnetic pole width is disclosed in Japanese Patent Laid-Open Publication No. 353616/99 (FIG. 9) and U.S. Pat. No. 6,043,959 (FIG. 16), wherein an upper magnetic layer is divided into a magnetic pole tip layer which defines the magnetic pole width and a yoke layer which is much wider. As another technique for fabricating a thin-film magnetic head having a small magnetic pole width, a trimming technique is disclosed in the above-described gazette and specification. In this technique, the magnetic pole tip of the upper magnetic layer is used as a mask for etching the recording gap layer and at least a portion of the magnetic pole tip of the lower magnetic layer facing the recording gap layer, whereby the sidewalls of the magnetic pole tip of the upper magnetic layer, the recording gap layer, and the portion of the magnetic pole tip of the lower magnetic layer are aligned. Dry etching is used in the above-described etching.
As another known technology for fabricating a thin-film magnetic head having a small magnetic pole width, Japanese Patent Laid-Open Publication No. 028626/94 (FIG. 5) and Japanese Patent Laid-Open Publication No. 314413/94 (FIG. 1) disclose methods in which the shapes of the magnetic pole tip layer of the lower magnetic layer, the recording gap layer, and the magnetic pole tip layer of the upper magnetic layer are aligned. In this technology, the magnetic pole tip layer of the lower magnetic layer, a recording gap layer, and a magnetic pole tip layer of the upper magnetic layer are successively formed using one photoresist frame by plating method.
Another problem also exists that the recording characteristics deteriorate when the magnetic pole width which defines the recording track width is reduced in order to increase the recording density. In other words, a reduction of the magnetic pole width is accompanied by a reduction in the size of the magnetic pole tip, whereby the area of contact is decreased between these tips and the lower magnetic layer and the upper magnetic layer. As a result, the magnetic flux which is generated in the lower magnetic layer and upper magnetic layer is not effectively conveyed to the magnetic pole tips, resulting in degradation of the recording characteristics, thus leading to deterioration of overwrite characteristic which indicates the performance of overwriting.
Thus, increasing the contact area between the magnetic pole, the lower magnetic layer and the upper magnetic layer is effective for preventing deterioration of the recording characteristic. Alternatively, shortening the throat height is also effective for reducing the loss of magnetic flux. From these standpoints, a technique is disclosed in Japanese Patent Laid-Open Publication No. 118214/2001 (FIG. 3) in which a magnetic pole is formed along a curved insulation. In this configuration, an insulating layer for defining the throat height is formed on the base of the lower magnetic layer, following which a photoresist frame is formed, the photoresist frame then being used in a plating method for forming the magnetic pole tip layer of the lower magnetic layer, the recording gap layer, and the magnetic pole tip layer of the upper magnetic layer. The throat height is the length (height) from the air bearing surface to the position at which the gap between the two magnetic layers begins to open.
When the magnetic pole width is controlled by trimming the magnetic pole tip as shown in Japanese Patent Laid-Open Publication No. 353616/99 and U.S. Pat. No. 6,043,959, the magnetic pole width is controlled by dry etching. This arises the problem that the magnetic pole width in a plurality of thin-film magnetic heads which are fabricated from a single wafer widely varies.
In contrast, when one photoresist frame is used to form the magnetic pole tip layer of the lower magnetic layer, the recording gap layer, and the magnetic pole tip layer of the upper magnetic layer as shown in Japanese Patent Laid-Open Publication No. 28626/94 or Japanese Patent Laid-Open Publication No. 314413/94, the magnetic pole width is controlled by photolithography. In this case, the variation in the magnetic pole width in a plurality of thin-film magnetic heads which are fabricated using a single wafer can be greatly suppressed than in a case in which the magnetic pole width is controlled by dry etching. In addition, the photoresist frame can be formed accurately if the photoresist frame is formed on a flat surface. Accordingly, when a photoresist frame is formed on a flat surface to form the magnetic pole tip layer of the lower magnetic layer, the recording gap layer, and the magnetic pole tip layer of the upper magnetic layer, variation in the magnetic pole width can be further suppressed.
Nevertheless, in a thin-film magnetic head which is fabricated using the techniques disclosed in Japanese Patent Laid-Open Publication No. 28626/94 and Japanese Patent Laid-Open Publication No. 314413/94, the throat height is equal to the distance from the air bearing surface to the opposite end on the assembly of the magnetic pole tip layer of the lower magnetic layer, the recording gap layer, and the magnetic pole tip layer of the upper magnetic layer. As a result, when the above-described distance is long in a thin-film magnetic head, the throat height is also long, whereby magnetic field sufficiently strong for recording may not be generated at the air bearing surface. On the other hand, when the above-described distance is short, the contact area between the upper and lower magnetic pole tip layers and the upper and lower yoke layers is reduced, sufficient magnetic flux cannot be supplied to the magnetic pole tip layers from the yoke layers, whereby magnetic field sufficiently strong for recording may not be generated at the air bearing surface.
In the technique which is disclosed in Japanese Patent Laid-Open Publication No. 118214/2001, the photoresist frame is formed, not on a flat surface, but on a stepped surface produced by the insulating layer which defines the throat height. The photoresist frame is therefore difficult to be formed with accuracy, and when using this technique, the problem arises that variations in the magnetic pole width are difficult to be suppressed when the magnetic-pole width is as small as 0.3 μm.